Current communications technology has adopted optical transmission of data as the medium of choice to obtain the benefits of high bandwidth transmission. As bandwidth increases for transmission through optical network elements, the reliability of the various elements becomes more critical. Although optical signals are known to be less prone to noise or interference, and thus more pure than electrically transmitted signals, the reliability and quality of the optical signal is also more critical because of the volume of data carried. The need for nearly one hundred percent availability drives network cost to a significant extent as it relates to the requirement for redundant equipment and its management to identify and restore a degraded signal within a network. It is generally accepted that a two-fold growth in bandwidth requires a two-fold increase in availability.
A highly available and reliable system involves component and interface redundancy, fault monitoring, and protection switching. Each of these functions is, in turn, available based on the following factors: component reliability, component redundancy ratio, protection switching speed, protection switching availability, failure detection speed, and detection mechanism availability.
An optical signal network system designed with adequate availability is more complicated than a similar electrical signal system because fault detection is necessarily at the optical signal level and localization of system faults involves a significant effort.
Therefore, it is an object of the present invention to provide an automatic optical signal quality selection system that does not require the optical signal to be converted into an electrical format for evaluation.
It is a further object of the present invention to provide an optical signal quality selection system able to discern between signals having different levels of degradation faster than an external system can detect the degraded signal.
It is another object of the present invention to provide an optical signal quality selection system able to delete an unacceptable quality signal and to transmit a signal after determining that its quality is acceptable.
It is another object of the present invention to provide an optical signal quality selection system able to inject an optical idle signal when no active signal is being transmitted through the system.
These and other objects will become more apparent from the description of the invention to follow.